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It shouldn't have to be reset, if it happens again I would dig a little deeper if not it could've been a fluke (power surge, power flicker etc)

Ok, Service Tech came out this AM, said it sounds like the flu pressure switch is tripping. There wasn't any codes stored since we were instructed to reset the furnace by turning the circuit breaker on/off/on.

When he went down to check it out, the furnace turned ON without him even touching anything. I was standing right behind him and could verify this. We were both like "WTHeck" ? He powered off the furnace (safety switch installed outside the cabinet), took off the top front cover. He said the switch (looked like a hockey puck) mounting plate was bent a bit and could have been rubbing against the cabinet. That's the only thing he could see as a possibility.

He showed me the troubleshooting lights and to call him with the codes if anything should happen.

The house was 57 degrees and T-Stat set at 70 degrees..... Furnace ran fine until it hit 66 degrees and shut OFF. Normally, it would go to 70 degrees and shut off.

I went down below to see if there were any Codes to read. There were NO lights what-so-ever. A few minutes passed and the furnace kicked back ON. It was OFF for around (20) minutes or so.

Any idea WHY the furnace would now shut off 4 degrees BEFORE the setting when it did NOT before hand ?

BTW, I believe I forgot to mention about that the Tech did replace the T-Stat last week with a digital type. Model Pro 1 IAQ T701 1 Stage.

It's tripping either a high temp limit from long run times with inadequate duct, low fan speed, dirty filter, or some type of air flow restriction or the vent pipe is too small or too long or without the correct pitch. Could be done other things but this gives you an idea.

It's tripping either a high temp limit from long run times with inadequate duct, low fan speed, dirty filter, or some type of air flow restriction or the vent pipe is too small or too long or without the correct pitch. Could be done other things but this gives you an idea.

ok.... I'll post pics of the furnace/install a bit later today.

The chimney is clear for sure (cleaned it out last year) so I now that is not the issue. The vent pipe off the furnace is the same diameter as the initial connection point (furnace), it does bend up a few feet and is spliced into the larger diameter flu pipe that goes to the chimney.

Furnace still running since my last posting (14 minutes ago)..... 68 degrees in here.....T-Stat at 70...

What's the complete model # of the furnace? Need to know size to see if duct is too small. 2-12" metal pipes with straight runs will provide approximately 1200cfm which is enough for a 3 ton ac or ~70kbtu gas furnace. How big are the return air grilles? They will add restriction if too small, of its flexible duct they cause restriction as well.

What's the complete model # of the furnace? Need to know size to see if duct is too small. 2-12" metal pipes with straight runs will provide approximately 1200cfm which is enough for a 3 ton ac or ~70kbtu gas furnace. How big are the return air grilles? They will add restriction if too small, of its flexible duct they cause restriction as well.